Dielectric properties of plasma sprayed titanates

Abstract

This paper presents the study of the dielectric properties of three plasma-deposited titanates. The deposits were prepared from powders with the same starting composition as industrially produced dielectric ceramics. Influence of plasma spraying itself and of the subsequent annealing of sprayed deposits on electric resistivity, permittivity and the loss factor is reported. Pure synthetic perovskite (CaTiO 3 ) and two perovskite-related ceramic materials (MgTiO 3 -CaTiO 3 and LaMg 0.5 Ti 0.5 O 3 -CaTiO 3 ) were plasma sprayed to form specimens enabling various electric measurements. CaTiO 3 and their solid solution with LaMg 0.5 Ti 0.5 O 3 have perovskite crystal structure and MgTiO 3 have the ilmenite structure. Water-stabilized plasma gun WSP 1 as well as commercial APS (gas stabilized system) were used to form ceramic layers on stainless steel substrates as well as self-supporting ceramic discs. Surface of specimens was ground after spraying. Thin layer of aluminum as the counter-electrode was sputtered in reduced pressure on the ground surface. Micrometric capacitor and ASTM-convenient resistivity adapter were used for voltage applying. Permittivity and volume resistivity were calculated from the measured capacity and resistance respectively. Self-supporting ceramic deposits were annealed at two different temperatures below and above the sintering temperature of the given material. Properties dependence on annealing temperature was obtained and discussed in relation to porosity. #

Dielectric relaxation in calcium titanate-containing ceramics prepared by plasma spraying

“…This fact is evident for low as well as for higher frequencies. Table 2 confirms from the point of view of the permittivity-frequency relationship the previously [7] drawn conclusion: there does not exist a medium filling voids (thereby able to penetrate into them during plasma spraying), which could be responsible for the whole magnitude of the difference between permittivity measured on as-sprayed versus sintered samples. The explanation of them probably must be looked for in structural features like grain boundaries arrangement introduced by the plasma spraying process to the material.…”

“…The water represents the case that water vapor condensed in voids at deposit cooling. The values in the first and last column of Table 2 were calculated according the two-component dispersion rules described in [16], but application of other rules like the Lichtenecker logarithmic formula [7] in principle gives the same results. The porosity of the deposits used here as water or air content is based on image analysis results [14].…”

“…First of all, they were examined from the point of view of their sprayability, chemical as well as phase composition, microstructure [5] and mechanical [5] as well as thermal properties [6]. Additional work resulted in a basic study of selected dielectric properties [7].…”

Influence of chemical composition on dielectric properties of Al2O3 and ZrO2 plasma deposits

“…The results indicate that plasma spraying does not introduce into those materials any special polarization ability or dielectric response instability as happened with all preliminary studied materials by the authors [22][23][24][25]. There is also no serious reason to support the statement [18] that moisture adsorbed within the voids is responsible for differences between the values of plasma deposited and sintered ceramics.…”

“…The authors' approach utilizes experiences gained on titanates and silicates [21][22][23][24][25]. In their opinion no materials exist which are absolutely suitable for a comprehensive study of the behavior of plasma sprayed ceramics in general in the electric field.…”